1. Field of the Invention
This invention relates to a head tracking system and, more particularly, to novel and highly-effective head moving apparatus that is suitable for use in electronic still video reproducing apparatus wherein video signals of a still image are recorded on a magnetic disk.
2. Description of the Prior Art
There is already known an electronic still camera in which an image of an object to be photographed is picked up by a solid state image pickup device such as a CCD and video signals representing the still image of this object are recorded on a magnetic disk. In such an electronic still camera, when the shutter button is pressed, the video signals of one field or one frame are read out of the solid state image pickup device. The luminance signal Y in the video signals is frequency modulated. The color difference signals (R-Y) and (B-Y) are line sequenced and frequency modulated. The video signals of one field are recorded on a single circular track.
In reproducing a still image, a particular recording track containing the video signals representing a desired still image is selected or designated from a plurality of circular recording tracks formed on the magnetic disk. When the track is thus selected or designated, the head is moved to the selected or designated track. Since the video signals of one field are recorded on one track, a desired still image is reproduced by continuously reproducing the video signals on the designated track in the case of the field recording mode. On the other hand, in the case of the frame recording mode, a desired still image is reproduced by alternately continuously reproducing the video signals on the designated track and the video signals on the subsequent track.
In a conventional electronic still video reproducing apparatus, when a desired still image is reproduced in this manner, a tracking control is performed so that the head can trace the center of a desired track. Such a tracking control has been disclosed in, e.g., U.S. Pat. No. 4,630,144. FIG. 1 appended hereto shows a tracking circuit in a conventional electronic still video reproducing apparatus. In FIG. 1, reference numeral 41 denotes a magnetic disk on which video signals of one field are recorded on each of the circular tracks and 42 indicates a head for reproducing the signals recorded on the magnetic disk 41. The magnetic disk 41 is rotated by a spindle motor 43. The head 42 is moved by a drive motor 44. A stepping motor is used as the drive motor 44.
The drive motor 44 is rotated on the basis of the number of pulses which are generated by a motor controller 45. A signal representing a designated moving amount which is derived by a head position operating circuit 46 is supplied to the motor controller 45. The motor controller 45 generates a number of pulses corresponding to this designated moving amount. These pulses are supplied to the drive motor 44.
When a track designation signal is supplied from a terminal 47 to the head position operating circuit 46, the amplitude of the head movement or head moving amount required for the head to reach the central position of a selected or designated track (hereinafter, this position is referred to as a mechanical center), which is determined in accordance with a predetermined format, is derived by the head position operating circuit 46. The head moving amount thus derived is supplied from the circuit 46 to the motor controller 45. Pulses of a number corresponding to the designated moving amount are generated by the motor controller 45 and supplied to the drive motor 44. Thus, the head 42 is moved to the mechanical center of the designated track.
After the head 42 is moved to the mechanical center of the designated track, the video signals on this track are reproduced by the head 42. The reproduced RF signal is supplied through a reproducing amplifier 48 to a signal processor (not shown) to reproduce the video signals and is also supplied to a peak level detector 49. The head 42 is moved radially inwardly or outwardly with respect to the disk one step at a time. One step corresponds to, e.g., 10 .mu.m. As the head 42 moves, the RF signal level changes. The position at which the maximum RF signal level is detected is the position at which the tracking is correctly performed. It is determined by the peak level detector 49 whether or not the RF signal level has reached the maximum level.
The level or strength of the reproduced RF signal before the head moves by one step is stored in the peak level detector 49. The reproduced RF signal level before the head is moved and the RF signal level after the head is moved by one step are compared by the peak level detector 49. A comparison output is supplied to the head position operating circuit 46. The head 42 is moved in accordance with the comparison output.
When the reproduced RF signal level after the head moves by one step is greater than the reproduced RF signal level before the head moves, this means that the head has moved towards the center of the recorded track. As long as this result is obtained, the apparatus continues to move the head 42 step by step in the same direction.
When the reproduced RF signal level after the movement of the head by one step is less than the reproduced RF signal level before the movement of the head, this means that the head has moved away from the center of the recorded track. In this case, the head 42 is then moved step by step in the opposite direction.
By performing the foregoing control, the apparatus ensures that the head 42 traces the center of a desired track. After the tracking has been correctly established, reproduction is executed.
As described above, in the conventional electronic still video reproducing apparatus, when a track is selected or designated, tracking control is performed so that the head traces the center of a desired track, and thereafter reproduction is started. A time of, e.g., about 130 msec is needed for establishing proper tracking. A still image cannot be reproduced during this time. Therefore, in the conventional electronic still video reproducing apparatus, there is the problem that a substantial time elapses from the time when a desired track is selected or designated until the time when reproduction begins.